Just wondering if that is something we should look out for in the future, especially since "Use External Materials" says "(Legacy)". Does that mean it will likely get deprecated in the future?
Honestly I'm not sure. I've experienced it every time I import something in Unity ever since they updated that materials feature. The "legacy materials" option was the default before and it just imported all the materials directly. It's quite annoying but I haven't been able to pin point what the exact cause is.
Anytime you see something that says "Legacy" Unity intends to do away with it in the future, but usually it takes a couple years before they remove it entirely. Hopefully they make it easier to work with materials in the future.